PROJECT SUMMARY State of the art techniques result in 10-year solid organ graft loss of 50 to over 70% in cardiopulmonary organ transplantation. Establishment of donor-specific immunological tolerance (DSIT), a condition in which a recipient accepts a transplant without immunosuppression, while retaining the ability to fight infections, would reduce graft loss and transplant related complications. The only identified method of inducing robust tolerance involves Hematopoietic Cell Transplantation (HCT), usually in the form of bone marrow transplantation (BMT). Though long recognized as a means of inducing DSIT that provides all tolerogenic mechanisms, clinical translation has been limited due to the associated complications. Other avenues that are currently being explored include cell therapy using immunomodulating mature hematopoietic cells such as regulatory T cells. While promising, this approach may be more limited in its ability to modulate and prevent rejection responses. We propose that progenitor cell therapy, specifically using Myeloid Progenitor cells (MP) may be the best compromise in introducing multiple immunomodulatory cell types without all the complications associated with BMT. Our data to date clearly support this hypothesis. We have discovered that injection of MP can result in MP-specific tolerance, even though there may be only very low-level sustained MP engraftment. Cellerant Therapeutics has developed a clinical MP product (CLT-008) produced by short-term ex vivo expansion (MPC). These cells are currently being tested in a Phase II clinical trial aimed at preventing infections in patients undergoing chemotherapy. Uniquely, MPC induce robust and reproducible antigen-specific tolerance in our experimental model system, are clinically available, and have been associated with minimal to no side effects in current clinical trials. MPC constitute an ideal and innovative approach in tolerance induction protocols, preferred over efforts aimed at achieving high-level donor chimerism. The proposed research in phase II will focus on establishing non-lethal preconditioning protocols that will work with MPC in tolerance induction (Aim 1). Aim 2 will determine whether mixed MPC preparations, as the clinical grade cells are currently produced, are effective in protecting grafts. We will also develop a xenograft mouse model to test the ability of human MPC to protect human grafts and Aim 3 will focus on determining the biodistribution and persistence of MPC (derived cells) in order to determine critical sites and timing of tolerance induction. Meeting the milestones for these aims will set the stage for designing trials using the Cellerant MP product, in which the clinical potential of this approach can be established.